DEBT - CREDIT FACILITIES AND SHORT-TERM DEBT (Details) - USD ($)	9 Months Ended
	Jun. 30, 2023	Feb. 07, 2023	Sep. 30, 2022
NJR | Letter of Credit on Behalf of NJRES
Line of Credit Facility [Line Items]
Letters of credit outstanding, amount	$ 5,200,000		$ 9,700,000
NJNG | Letter of Credit
Line of Credit Facility [Line Items]
Letters of credit outstanding, amount	$ 731,000		731,000
Revolving Credit Facility | NJR
Line of Credit Facility [Line Items]
Commitment fee percentage	0.10%
Revolving Credit Facility | NJNG
Line of Credit Facility [Line Items]
Commitment fee percentage	0.075%
Revolving Credit Facility | Committed Credit Facilities Due September 2027 | NJR
Line of Credit Facility [Line Items]
Bank revolving credit facilities	$ 650,000,000		650,000,000
Amount outstanding at end of period	$ 134,525,000		$ 200,150,000
Weighted average interest rate at end of period	6.31%		3.97%
Amount available at end of period	$ 510,302,000		$ 440,177,000
Revolving Credit Facility | Committed Credit Facilities Due September 2027 | NJNG
Line of Credit Facility [Line Items]
Bank revolving credit facilities	250,000,000		250,000,000
Amount outstanding at end of period	$ 10,700,000		$ 73,800,000
Weighted average interest rate at end of period	5.25%		3.34%
Amount available at end of period	$ 238,569,000		$ 175,469,000
Term Loan | Committed Credit Facilities Due February 2023 | NJR
Line of Credit Facility [Line Items]
Bank revolving credit facilities	0	$ 150,000,000	150,000,000
Amount outstanding at end of period	$ 0		$ 150,000,000
Weighted average interest rate at end of period	0.00%		3.81%
Amount available at end of period	$ 0		$ 0